It is well known in motor vehicle passive occupant restraint systems to provide a belt carriage which is movable along a track by a motor-driven drive element to move the restraint belt between an occupant restraining position and a stowed position permitting occupant ingress and egress. A speed reduction gear unit is conventionally employed in connection with the electric motor and the drive element in order to provide the desired relatively low speed of movement of the carriage along the track.
In the event of malfunction of the drive motor or of the electrical control circuit therefor, the carriage will come to rest and accordingly the belt will remain poised in either the restraining position or the stowed position. It would be desirable to provide some arrangement by which the occupant may effect a manual movement of the belt carriage along the track. However, it is very difficult to effect such manual carriage movement because the speed reduction gear unit is not conductive to forced reverse rotation.
The present invention provides an improvement in the prior known motor-driven belt carriage systems by the provision of a centrifugal clutch mechanism providing the drive coupling between the motor-driven speed reduction gear unit and the belt carriage drive element so that the drive element is uncoupled except when the motor is energized to enable manual movement of the belt carriage along the track.